Flare and vent stacks are commonly used in the petroleum, chemical and petrochemical industry to dispose of combustible gases which either constitute waste material or which have had to be released to relieve excess pressure. These stacks are frequently provided with a liquid seal through which the gases pass. The purpose of the liquid seal includes the preventing of flame flashback, and the maintenance of an above-atmospheric pressure in the feedline leading to the stack. An above-atmospheric pressure is needed to prevent any possibility of air entering the feedline through faulty connections or the
For very large rates of gas flow, a horizontal vessel sometimes referred to as a "flare seal drum" is used, and is conventionally mounted alongside the stack to perform these functions.
In more detail, flaring apparatus is thus employed for flaring combustible gaseous materials, nd especially for the flaring and burning of gaseous hydrocarbon material where such materials are derived from operations for the refining of petroleum oils in various industrial operations, in which large volumes of combustible gaseous materials are produced. As is apparent, some of these materials have no real economic value as fuel or otherwise, and therefore must be disposed of in a suitable manner. Further, such materials result from upset conditions in the normal operation of a refinery wherein gases which ordinarily might be subjected to further processing in order to obtain valuable products therefrom must be vented in order to avoid the occurrence of dangerously abnormal pressures in operating equipment. The total volume of all such accumulations of gases in normal refinery operation and their hazardous nature make it impracticable for such gases to be discharged directly into the atmosphere. Thus, in practice, it is customary to burn such gases as they are discharged from an exhaust or flare stack at a considerable distance above the ground, although on occasion for the sake of economy, burning may be accomplished in relatively low large diameter enclosures or flare structures. The flare seal drum fits into the overall flaring apparatus in that it, as mentioned, prevents flashback, that is, it prevents a backfeed of the flame. Further, by preventing any backfeed of air the possibility of combustion is substantially eliminated, and thus an explosive situation is avoided.
The flare systems thus commonly installed at refineries and petrochemical plants, must be capable of smoothly carrying off the sudden waste gas surges occurring during operating disturbances and in emergencies. A flare system of the type described, generally consists of a collecting or inlet line in which the gases to be flared are passed by way of a liquid-containing drum connected to the flare which is designed as a high stack and/or as a ground level flare and from which the gases can be flared in so far as they are combustible. The liquid used may be water or, if required a glycol/water mixture.
For example, it is known to provide apparatus which has been referred to as a "water seal pot", which allows gases to flow through the water when the pressure in the supply line upstream of the water seal pot is greater than that which will displace the head of water above the point at which the gas is released. One of such known devices includes a tube which guides the gas into a vessel, the tube having an open end immersed in the liquid retained in the vessel. The gas, when supplied at pressures greater than those required to displace the head of water above the open free end of the tube, moves through the liquid. The flow of gas is not constant and the gaseous medium is discharged in the form of large bubbles. The bubbles of compressible gas within an incompressible liquid set up pressure surges both upstream and downstream of the seal pot. It is possible for these surges to vary sufficiently to cause instantaneous interruption of the flow of gases downstream of the water pot. Thus, for example, when a water seal pot of the type employed in the past is arranged in the gas supply line to a flare stack gas burner, the interruption in the flow of gases often causes a rapid extinction of the flame with corresponding rapid reignition, which cause the repeating of an objectionable "boom" upon each reignition of the gaseous medium.
Conventional designs of liquid-seal units used practice have serious disadvantages, e.g.:
The immersion liquid is affected during the whole period of the flaring operation by the quantity or pressure of gas involved. Excess pressures cause a liquid funnel (cone) to be formed.
The liquid funnel which is formed collapses again and again, and this gives rise to pulsation, causes an upsurge in the gas column in the flare and produces the familiar of a pulsatingly burning flare; this has the effect of increasing the noise level.
Serious problems arise in the operation of seal drums as a result of a pulsing flow of gas. The pulsing flow has a tendency to cause the flare to go out, and then to be reignited, as mentioned, and a resulting booming sound which is objectionable. Furthermore, increased smoking at the flare may occur, and this requires the injection of additional amounts of steam into the flame. Not only is this wasteful of energy, but it results in a rumbling sound which is rather loud and, like the booming, is disturbing to the neighborhood. From the standpoint of efficiency, economy and public relations, therefore, it is important to eliminate, or at least to suppress, gas pressure surges to the flare Many prior devices have been proposed for this purpose and, while they are to some degree effective, these prior devices fall short of successfully solving the problem.
Typical of proposals of this type generally involve systems for distributing the gas through a plurality of open outlets or ports. Typical constructions are shown, for example, in Reed U.S. Pat. Nos. 3,064,956, 3,231,252, and 3,606,985, and in U.S. Pat. No. 3,595,260.
It is, accordingly, an object of the present invention to provide a seal drum construction for a flare which effectively suppresses the heretofore encountered negative effects of pulsing flow.
It is another object of the invention to provide a flare seal drum of the character indicated wherein any variations pressure in the incoming gas flow are effectively accommodated, and pulsing flow to the flare is minimized.
It is a still further object of the invention to provide a flare seal drum construction of the character indicated, wherein the pulsing-suppressing action occurs automatically at all times, and does not require the intervention of an operator.